Heart Anatomy

Heart Anatomy

Location

• Snugly enclosed within the middle mediastinum (medial cavity of the thorax)
  • Contains the heart, pericardium, vessels to & from the heart & lungs, trachea & esophagus.
  • M.Mediastinum – located in the inferior mediastinum (lower than the sterna angle)
• Extends obliquely from 2nd rib à 5th intercostals space.
• Anterior to Vertebrae
• Posterior to Sternum
• Flanked by 2 lungs
• Rests on the diaphragm
• 2/3 of its mass lies to the LHS of the midsternal line.

The Pericardium: (Coverings of the Heart)

• A double-walled sac
• contains a film of lubricating serous fluid
• 2 Layers of Pericardium:

Fibrous Pericardium:

• Tough, dense connective tissue
• Protects the heart
• Anchors it to surrounding structures
• Prevents overfilling of the heart – if fluid builds up in the pericardial cavity, it can
• inhibit effective pumping. (Cardiac Tamponade)

Serous Pericardium: (one continuous sheet with ‘2 layers’)

• Parietal Layer – Lines the internal surface of the fibrous pericardium
• Visceral Layer – (aka Epicardium) Lines the external heart surface

Layers of the Heart Wall:

Epicardium

• Visceral layer of serous pericardium

Myocardium

• Muscle of the heart
• The layer that ‘contracts

Endocardium

• Lines the chambers of the heart
• Prevents clotting of blood within the heart
• Forms a barrier between the O2 hungry myocardium and the blood. (blood is supplied via the coronary system)

Fibrous Skeleton of the Heart

• The network of connective tissue fibers (collagen & elastin) within the myocardium
• Anchors the cardiac muscle fibers.
• Reinforces the myocardium

2 Parts

Septums:

• Flat sheets separate atriums, ventricles & left and right sides of the heart.
• Electrically isolates the left & right sides of the heart (conn. Tissue = non-conductive)
  • Important for cardiac cycle
• (interatrial septum/atrioventricular septum/interventricular septum)

Rings:

• Rings around great vessel entrances & valves
• stop stretching under pressure

Chambers & Associated Great Vessels

2 Atrias (superior): [Atrium = Entryway]

• Thin-walled Receiving Chambers
• On the back & superior aspect of the heart.
• Each has a small, protruding appendage called Auricles – increase atrial volume.
• Septal Area
  • Connective tissue dividing L & R atria. (Site of Foetal Shunt Foramen ovale)
• Right Atrium:
  • Smooth internal posterior wall
  • Where veins drain into (either from body/lungs)
  • Ridged internal anterior wall – due to muscle bundles called Pectinate Muscles.
  • Blood enters via 3 veins:
  • Superior Vena Cava
  • Inferior Vena Cava
  • Coronary Sinus (collects blood draining from the myocardium)
• Left Atrium:
  • Smooth internal post. & ante. walls.
  • Blood enters via:
    • The 4 pulmonary veins (O2 blood) [Pulmonos = Lung]

2 Ventricles (inferior): [Vent = Underside]

• Thick, muscular Discharging Chambers
• The ‘pumps’ of the heart
• Trabeculae Carnea [crossbars of flesh] line the internal walls
• Papillary Muscles play a role in valve function.
• Right Ventricle:
  • Most of the heart’s Anterior Surface
  • Thinner – responsible for the Pulmonary Circulation – Via Pulmonary Trunk
• Left Ventricle:
  • Thicker – it is responsible for the Systemic Circulation – Via Aorta
  • Most of the heart’s PosteroInferior Surface

Landmarks of the Heart:

• Coronary Sulcus (Atrioventricular Groove):
  • Encircles the junction between the Atria & Ventricles like a ‘Crown’ (Corona).
  • Cradles the Coronary Arteries (R&L), Coronary Sinus, & Great Cardiac Vein
• Anterior Interventricular Sulcus:
  • Cradles the Anterior Interventricular Artery
  • Separates the right & left Ventricles anteriorly
  • Continues as the posterior Interventricular Sulcus.
• Posterior Interventricular Sulcus:
  • Continuation of the Anterior Interventricular Sulcus
  • Separates the right & left Ventricles posteriorly

Pathway of Blood Through the Heart:

The systemic and pulmonary circuits:

• The right side of the heart pumps blood through the pulmonary circuit (to the lungs and back to the
• the left side of the heart).
  • Blood flowing through the pulmonary circuit gains oxygen and loses carbon dioxide,
• indicated by the color change from blue to red.
• The left side of the heart pumps blood via the systemic circuit to all body tissues and back to the
• the right side of the heart.
  • Blood flowing through the systemic circuit loses oxygen and picks up carbon dioxide (red to
• blue color change)

Coronary Circulation

• The myocardium’s own blood supply
• The shortest circulation in the body
• Arteries lie in the epicardium – prevents the contractions inhibiting blood flow
• There is a lot of variation among different people.

Arterial Supply

• Encircle the heart in the coronary sulcus
• Aorta – Left & Right coronary arteries
  • Left Coronary Artery – 2 Branches:
    • 1. Anterior InterVentricular Artery (aka. Left Anterior Descending Artery …or LAD).
      • Follows the Anterior InterVentricular Sulcus
      • Supplies blood to InterVentricular Septum & Anterior walls of both Ventricles.
    • 2. Circumflex Artery
      • Follows the Coronary Sulcus (aka. AtrioVentricular Groove)
      • Supplies the Left Atrium & Posterior walls of the Left Ventricle
• Right Coronary Artery – 2 (‘T-junction) Branches:
  • 1. Marginal Artery:
    • Serves the Myocardium Lateral RHS of Heart
  • 2. Posterior Interventricular Artery:
    • Supplies posterior ventricular walls
    • Anastomoses with the Anterior Interventricular Artery

Venous Drainage:

• Venous blood – collected by the Cardiac Veins:
  • Great Cardiac Vein (in Anterior InterVentricular Sulcus)
  • Middle Cardiac Vein (in Posterior InterVentricular Sulcus)
  • Small Cardiac Vein (along Right inferior Margin)
    • – Which empties into the Right Atrium.

Heart Valves:

• Ensure unidirectional flow of blood through the heart.
• 2x AtrioVentricular (AV) (Cuspid) Valves:
  • Located at the 2 Atrial-Ventricular junctions
  • Prevent backflow into the Atria during Contraction of Ventricles
  • Attached to each valve flap are chordae tendinae (tendonous cords) “heart strings”
    • Anchor the cusps to the Papillary Muscles protruding from ventricular walls.
      • Papillary muscles contract before the ventricle to take up the slack in the chordae tendinae.
      • Prevent inversion of valves under ventricular contraction.
• Right AV Valve:
  • The “Tricuspid Valve”
  • 3 flexible ‘cusps’ (flaps of endocardium + Conn. Tissue)
• Left AV Valve:
  • The “Mitral Valve” or “Biscupid Valve”
  • (resembles the 2-sided bishop’s miter [hat])

• 2x SemiLunar (SL) Valves:
  • Guard the bases of the large arteries issuing from the Ventricles.
  • Each consists of 3 pocket-like cusps resembling a crescent moon (semilunar = half moon)
  • Open under Ventricular Pressure
  • Pulmonary Valve:
    • Between Right Ventricle & Pulmonary Trunk
  • Aortic Valve:
    • Between Left Ventricle & Aorta

Valve Sounds:

• 1. “Lubb”:
  • Sound of a Cuspid Valve closing
• 2. “Dupp”:
  • Sound of a Semilunar Valve Closing
• Where to Listen: